A large slug unlikely to be confused regionally, up to 80 mm extended. Dorsal base color tan with scattered brown to black markings of varying density throughout and an irregular brown to black stripe on either side of the mantle, the mantle smooth and covering 2/3 or more of the body. Anterior quarter of the mantle is free from the head. The pneumostome is slightly posterior to the midline of the mantle on the right side. The tail is unkeeled and the sole undivided (not tripartite); the mucous is clear. Disturbed individuals may flare the anterior portion and sides of the mantle out and upward (Hendricks 2012, Burke 2013). Internal anatomy is described by Pilsbry and Brunson (1954) and Webb and Russell (1977).

Diagnostic Characteristics

A combination of size, body morphology and markings differentiate this species from other slugs in Montana. The length of the mantle (> 2/3 of the body length) is unique.

Species Range

Montana Range

Year-round

Range Comments

Southeastern British Columbia, northeastern Washington, northern Idaho and adjacent northwestern Montana west of the Continental Divide (Burke 2013). In Montana, 35 records in seven counties: Flathead (3), Granite (3), Lincoln (7), Mineral (4), Missoula (11), Ravalli (2), Sanders (5). Elevation range is 840 to 2211 m (2756 to 7254 ft). Originally described from a specimen near Lolo Pass in Clearwater County, Idaho. Can be locally abundant; 32 individuals were found at one Missoula County, Montana site in late May and 86 at another in early June (Hendricks 2012).

(Observations spanning multiple months or years are excluded from time charts)

Predicted Distribution in Montana
Predicted distribution model for Magnum Mantleslug (Magnipelta mycophaga).
Records were spatially unique and had a locational uncertainty of ≤ 400 meters.
Hotter colors indicate areas that are predicted to have more suitable habitat for the species.
Black dots are positive data used to build the model.
Gray dots are locations where a survey capable of detecting the species has been performed.
Landownership, a shaded relief map, and county lines are included for reference.
Details of the modeling effort, a description of the environmental layers used, and a more thorough interpretation
of model outputs can be found in the report Land Mollusk Surveys and Predicted Distribution Models on USFS Northern Region Lands: 2007.

Omission and Predicted Area
An evaluation of omission error rates for training data as a function of the cumulative threshold and overall predicted area.
The red line indicates the overall fraction of the map area fitting each value of the cumulative threshold.
The light blue line is the predicted omission error rate for each cumulative threshold.

Receiver Operating Characteristic Curve
Receiver Operating Characteristic (ROC) curve evaluating the overall predictive power of the model with the Area Under the Curve (AUC).
The AUC value indicates that when two random locations are chosen the model has that probability of assigning a higher cumulative threshold value to the location with more suitable habitat.
The light blue line indicates how a neutral or random model would perform (i.e., it only has a 50% probability of assigning a higher cumulative threshold value to a random location with more suitable habitat than a random location with less suitable habitat).
The further toward the top left of the graph the red training data line is, the better the model is at predicting the presences contained in the training data.
Sensitivity (plotted on the y-axis) is the proportion of positive locations that were correctly classified by the model.
Sensitivity is also known as the true positive rate and can be thought of as the degree of absence of omission errors.
Specificity is the proportion of random locations chosen from the background (these pseudo-absences are used instead of true negative locations) that were correctly classified by the model as negative.
One minus the Specificity (plotted on the x-axis) is known as the false positive rate and represents the commission error rate.

Environmental Variable Response Curves
Response curves for individual environmental variables showing how the logistic prediction changes as each environmental variable is varied while all other environmental variables are held constant at their average sample values.
The value on the y-axis is predicted probability of suitable conditions as given by the logistic formula

Jackknife Chart
Jackknife chart showing the relative importance of environmental variables as a function of the change in “gain” (the log of the number of grid cells minus the average of the negative log probabilities of the sample locations) resulting from the exclusion or sole inclusion of the environmental variable in the model.
Variables with the highest training gain resulting from sole inclusion of those variables (dark blue bars) are the best individual variables at describing suitable habitat for the species.
Variables with the greatest reduction in training gain resulting from their exclusion (light blue bars) contain information on the species habitat use that is not present in other variables.
The red bar indicates the maximum gain achieved with inclusion of all variables.

Habitat occupied by Magnipelta mycophaga (moderate elevation mixed conifer forest, especially spruce-fir, often near water) is threatened by logging, grazing, fire, possibly rural home development, and possibly recreation and weed control. The impact of fire retardant on this and other terrestrial mollusks is not known. Little is known about this species, including sensitivity to disturbance.

References

Literature Cited AboveLegend: View Online Publication

Burke, T. E. 2013. Land snails and slugs of the Pacific Northwest. Corvallis, OR: Oregon State University Press. 344 p.

Hendricks, P. 2012. A Guide to the Land Snails and Slugs of Montana. A report to the U.S. Forest Service - Region 1. Montana Natural Heritage Program, Helena, MT. vii + 187 pp. plus appendices.

Forrester, Donald J. 1962. Land Molluska as Possible Intermediate Hosts of Protostrongylus stilesi, a Lungworm of Bighorn Sheep in Western Montana. Proceedings of the Montana Academy of Sciences, 22: 82-92.

Forsyth, R.G. 2004. Land snails of British Columbia. Royal British Columbia Museum: Victoria, British Columbia, Canada. 188 pp.